Spodoptera littoralis

Scientific Name Spodoptera littoralis (Boisduval) , S. litura (Fabricius)
Synonyms These two species were formerly considered as one, then called Prodenia litura. Due to their similarity, they are still treated together in this text.
Common Names English: Egyptian cotton leafworm, cotton worm; German: Afrikanischer Baumwollwurm; Spanish: Rosquilla negra; French: Ver du cotonnier, Prodénia
Description The forewings are brown with irregular markings, and they span up to 40 mm (1.57 inch). The hind wings, visible when spread, are whitish with darker margins.

The caterpillar is variable in color, from dark green to blackish-gray or brown, with longitudinal stripes; it is hairless, and, when fully developed, up to 50 mm (1.97 inch) long.

Biology

Damage

The larvae of the cotton leafworm feed voraciously on almost all plant organs. Generally, young leaves are preferred, but when they have been consumed, other parts (e.g. stems, buds or pods) are attacked too. An infestation frequently leads to complete defoliation. Besides devouring the leaves, the caterpillars interfere with plant development by destroying growth points and flowers.
They bore into buds and fruits and feed inside them, soiling them with frass. In cotton, the bolls will be hollowed out, which often causes them to wilt and drop. In tomato, capsicum and similar crops, fruits that are attacked in this way are not only severely damaged, but also contain a lot of excrement and thus become unsuitable for human consumption. In corn, the larvae mine inside the stems and may feed on young kernels in the ear.
On light soil, they can continue feeding during the daytime, when they hide underground. In this case, subterranean plant parts (e.g. the pods and kernels of groundnut) will be attacked. Root vegetables may become unmarketable due to large holes.

Lifecycle

Eggs are laid in batches of several hundred on the plant surface. Each egg mass is of about 3-7 mm (0.12-0.27 inch) diameter and appears hairy, because the female covers it with brownish-yellow scales produced from the tip of its abdomen. Fecundity is high: about 2,000-3,000 eggs are produced over a 6-8 day period.
Two to five days after oviposition, the larvae hatch and quickly disperse over their host plant. Normally, there are six larval instars. The older ones feed only at night and hide in the soil during the day. When they have exhausted their food source, the caterpillars sometimes migrate in large numbers towards other, as yet undamaged plants. Pupation, too, takes place in the soil, about 2-5 cm (0.78-1.97 inch) deep, inside a loose cocoon, and lasts about 7-10 days. The adults are active at night and mate several times.
The development times can sometimes be much longer at lower temperatures; eggs may need up to 10 days, the larvae three months and pupation 4 weeks. If this is the case, there may be an additional instar. This occurs for example in areas where cotton leafworm is only found in glasshouses. It can diapause in the pupal stage, but cannot withstand repeated frost. In the tropics, more than 12 generations per year are possible and population densities may become huge. In Egyptian cotton fields, several 10,000 egg masses per acre have been counted.
The two species are allopatric, i.e. their ranges do not overlap. Spodoptera littoralis is found in Africa and Southern Europe, whereas S. litura occurs throughout Asia, Australasia and the Pacific Islands and was accidentally introduced to Europe in 1963. It is not quite certain, however, that all reports of cotton leafworm from European glasshouses actually refer to S. litura and not to S. littoralis.

Occurrence

Additional Crop Information

Both species are extremely polyphagous and attack over a hundred important crops, among them such different ones as alfalfa, apple, artichoke, aubergine, banana, cabbage, capsicum, carrot, cotton, cucurbits, geranium, grapevine, groundnut, jute, lettuce, corn, onion, potato, rice, soybean, tea, tomato and many others.

Agricultural Importance

One of the most destructive of insect pests due to its enormous host range, voracity and reproductive potential.

Control

Useful non-chemical contribution to Integrated Weed Management

Removing harvest residues will expose pupae to predators and the sun.

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